Land erosion in the Mekong Delta must be carefully considered

A group of local officials examine a land erosion site in Hậu Giang Province's Châu Thành District in the Mekong Delta last week. — VNA/VNS Photo Hồng Thái

Nguyễn Hữu Thiện, an independent researcher on the ecosystem in the Mekong Delta talks to Nông thôn Ngày nay (Countryside Today) newspaper on the serious problem of land erosion in the region.

Is soil erosion common along river banks in the Mekong Delta?

The Mekong Delta was formed by sand and alluvial soil over the last 6,000 years. In that process, it is natural to see along the river banks an extending side and a sliding side.

However, the extending side is always wider than the sliding side. That’s why the Cửu Long Delta has become larger and larger as times goes by. On average, each year, the Cửu Long Delta’s land grows 16 metres towards the East Sea, while in the mainland it also gains some 26 metres per annum towards the direction of the Cà Mau Cape. However, in the last 25 years, since 1992, the issue of land erosion has intensified. Particularly, since 2005, the coastal area in the Mekong Delta has switched from gaining land to losing land. It is estimated that each year, the Mekong Delta loses some 50 metres, causing a serious threat to people living along the river banks in the region.

What are the main causes behind the problem?

The mean reason is the shortage of sand while alluvial land has been blocked by many hydropower dams and the mass exploitation of sand along the Mekong River which runs from Thailand to Laos, Cambodia and Việt Nam. However, the most serious problem is the massive sand exploitation occurring in Cambodia and Việt Nam. According to statistics from the International Commission of Mekong Sub Region, between 1992 and 2014, the total volume of fine alluvial soil of the Mekong River dropped 50 per cent – from 160 million tonnes down to 85 million tonnes.

For the river banks, when there is a shortage of alluvial soil, the water flow becomes much fiercer than normal. This is the main source of land erosion on one side and land reclamation on the other side. In addition, the over-extraction of sand has made the river bed deeper.

Are there any other causes leading to erosion in the Mekong Delta?

Other causes are only minor. For example, the weak soil can lead to land erosion. Another cause is the construction of major projects along the river banks.

People living along the Mekong Delta have started filling holes caused by land erosion. Should people do that?

Deep holes are a part of the natural development of the Mekong River system. It is reported that along the Mekong River system, there are 584 deep holes like those in the Mekong Delta – the deepest one is 90.5 metres, while the longest is 18km. These holes are also home to more than 200 species of fish, even in the dry season.

In the Mekong Delta, 22 holes have been surveyed by the International Mekong River Commission since 2008. These holes are different to man-made holes following sand extraction. So, they are not the culprits behind soil erosion.

Principally speaking, all the natural deep holes will be filled with sand from the water flow in the upper stream down to the lower stream. In September and October, when flood season comes, the water flow will make the holes deeper. That’s why we should not fill up these holes in order to keep the water flow stable.

What should functional agencies in the Mekong Delta do to limit the problem of land erosion?

I don’t think there is any single measure that can be done in the Mekong Delta to solve this problem. The root cause of the land erosion along the river banks is due to a shortage of alluvial soil and sand. That’s why projects will not be able to prevent the problem of land erosion, just delay it.

What should be done right now is to take actions to minimise the losses or damage to local people.

There are three options – first, to build projects in weak soil areas with heavy population and villages living along the river banks. Second, for people living in the countryside along the river banks, the local authorities should develop plans to persuade them to move to safer places. And the last option, authorities should develop a sound plan on sand extraction activities.

We should consider very carefully the option of building a concrete dyke system as just 1km of dyke would cost VNĐ100 billion (US$4.3 million). And I don’t think we have the money to do it. — VNS